A group of sensory scientists who have cooperated formally and informally for many years proposes to focus their joint research on specific, long- range problems of intensity effects and processing in the auditory and tactile systems. The broad goals of the project remain essentially unchanged from the first submission in 1986. However, the experience gained in the first two years of focusing on a single problem has resulted in a better integration of the component projects and clearer concepts of how two sensory systems, hearing and touch, may be related to a common theme. A multidisciplinary approach is being used, including 1) human and animal behavior, 2) neurophysiology, and 3) neuroanatomy, with the specific goal of providing definitive answers to still unresolved problems of transduction and intensity coding in the two sensory systems. Specific experiments within the sensory modalities run partially parallel and partially complementary courses, so that the three component projects are interlocked in their goals. The approach of systems analysis is being used. Global functions are determined from human psychophysics and animal behavior (Component Project 1). Project 1 experiments are focused on the relation between intensity discrimination and loudness, intensity effects in the discrimination of complex stimuli, and the correlation of behavioral and neural responses within the two modalities. The contributions of relevant components of the systems to the global functions are being sought through direct physiological (Component Project 2) and morphological (Component Project 3) experiments aided by mathematical analysis. Project 2 experiments concern the effects of stimulus intensity on the neural responses in the auditory and tactile periphery. Project 3 is targeted on the role in transduction and intensity effects played by the auditory hair- cells, eighth nerve and cochlear nucleus, and by the various receptor and fiber types in the peripheral tactile system. The experiments involve vertebrate animals, including humans. All of the proposed experiments are consistent with our group's expertise and long-range goals of elucidating questions of fundamental importance to our understanding of the neural mechanisms underlying human behavior.